The design of electronic circuits requires interconnections between devices for proper operation. With increased sophistication and operational speeds, the design and fabrication of functional interconnections requires careful engineering. The fastest data processing circuits and emerging technologies require large numbers of interconnects capable of carrying extremely high-speed signals. Due to the increasing push for higher and higher speeds, engineers are facing fundamental limitations in designing electronic interconnects.
In an attempt to handle higher signal speeds and increased data transmission rates, interconnection technology has turned to optical interconnects for the next generation of circuits. Optical circuits have bandwidth capabilities orders of magnitude beyond similar electronic circuits, and are inherently immune to electrical interference. In some known designs, discrete fiber optic cables and fiber bundles are used to interconnect devices. Known standard fiber optic connection technology employed to fabricate optical circuits and connect optical fibers to devices is adequate for small numbers of interconnections. However, as optical circuit density grows, the physical bulk of fiber optic cables and connectors makes current approaches unwieldy.
Fabrication of certain kinds of fiber-based optical circuits is known in the art. For example, it is known that optical circuits may be fabricated by adhesively bonding or embedding optical fibers, using pressure sensitive adhesives (PSA) or partially cured monomers coated on laminating films. The adhesive and optical fiber assembly can then be further protected by, for example, applying a cover layer, curing the adhesive, or flood coating and curing. In each case, the finished assembly consists of optical fibers held firmly in place in an intermediate layer of a multi-layer assembly.
However, there are certain problems associated with the use of adhesive, as used on coated films and the like. For instance, within the optical circuit, the optical fibers are firmly fixed in place. Once assembled, it can be difficult or impossible to add, remove, or replace a given optical fiber to repair or update the circuit design. In addition, the optical fibers embedded in such designs restrict the flexibility of the assembly, and the fibers may be placed under undesirable levels of stress if the assembly is bent or forced to conform to a non-planar surface. Fibers that cross over each other due to requirements of the circuit pattern may be subjected to microbending stresses and associated optical loss as the circuit layers are laminated together. Fibers rigidly held in such optical circuit assemblies may also exhibit increased bending loss caused by temperature-induced stress.
Attempts have been made to address the problems discussed above. In U.S. Pat. Nos. 5,902,435 and 6,427,034 to Meis, et al., flexible optical circuit appliqués that allow for repositioning of the optical circuits to achieve proper alignment are shown. The flexible optical circuit appliqués of Meis, et al., provide microstructures on a backing layer, such that the microstructures prevent the adhesive coating on the backing layer from immediately adhering to a substrate. In this manner, the optical fiber may be repositioned until proper alignment has been achieved. In one embodiment, upon application of appropriate force, the microstructures will crush and thereby allow the adhesive coating to bond the film to a substrate. The microstructures additionally provide a guide for routing optical fibers in precise locations as they are applied to the adhesive surface. However, some of the disadvantages of adhesive mentioned above still remain.
A need still exists for optical circuits that allow the addition, removal, or replacement of optical fibers in an optical circuit after its initial assembly, and that reduce or eliminate undesirable stresses, which lead to optical loss. A method of fabricating optical circuits that provide such benefits is also needed.